1. Technical Field
The invention relates to a method for driving a solid-state imaging device and an imaging apparatus, and more particularly, to the method for driving the solid-state imaging device in taking moving images or in controlling AE (automatic exposure)/AF (automatic focus), and the imaging apparatus.
2. Description of the Related Art
A solid-state imaging device has been frequently used in an electronic still camera, a digital imaging apparatus for moving images. Generally, in the electronic still cameras, AE (automatic exposure)/AF (automatic focus) control is performed prior to taking an image. If this control is performed using signal charges which have been accumulated in all pixels of the solid-state imaging device, it takes a long time to finish this control, and it is concerned that a good photographing opportunity may be missed. For this reason, it is required to increase a frame rate during the AE (automatic exposure)/AF (automatic focus) control to be almost several times as high as the frame rate for ordinary imaging.
Moreover, since even decrease in resolution during the AE (automatic exposure)/AF (automatic focus) control does not pose a problem, the frame rate has been increased by skipping image signals which are obtained by the solid-state imaging device. For moving images, demand for a resolution is not as strong as in the electronic still camera because images are moving. Also, a high frame rate is required in order to take moving images. Therefore, the control of skipping image signals has been performed for moving images. However, the skipping control causes such a problem that an amount of signal charges decreases and that sensitivity is lowered.
In order to deal with such a problem, for example, JP Hei. 11-261901 A (corresponding to U.S. Pat. No. 6,744,466) has proposed a method for driving a solid-state imaging device, the method including selectively reading signal charges from two pixel lines in a cycle of three vertical pixels lines, and adding the signal charges of the two pixel lines in a horizontal transfer section for output.
Also, several methods have been proposed for arranging photoelectric conversion elements of a solid-state imaging element. For example, JP 2004-55786 A (corresponding to US 2004/0017497 A) has proposed, as a arrangement other than a square lattice arrangement, a honeycomb arrangement in which odd-numbered rows and even-numbered rows of photoelectric conversion element rows are shifted by ½ pitch in a row direction and in a column direction.
However, according to the method for driving the solid-state imaging device described in JP Hei. 11-261901 A, the signal charges of the two pixel lines are selectively read in the cycle of three vertical pixels lines, the signal charges of the two pixel lines are added in the horizontal transfer section, and remaining pixel data which are not read are discarded. As a result, sensitivity is sacrificed, and moving images may become short of brightness in a dark environment, or accuracy of the AE/AF control may be deteriorated.